1. Field of the Invention
The present invention relates to a classifying tray apparatus wherein the sheets, discharged from an image forming apparatus such as a copying machine and printing machine, are classified and stacked by a sheet discharge tray that can move from side to side and can elevate.
2. Description of the Prior Art
In a conventional classifying tray apparatus having the classifying function, a sheet discharge tray is provided at a predetermined distance under a sheet discharging portion for discharging the sheet, the sheet discharge tray having a surface which is inclined upward in an outer direction such that the sheet discharge tray is drived to move in a direction perpendicular to a discharge direction (hereinafter referred to as a right-to-left direction).
The sheet discharged from the sheet discharging portion falls onto the sheet dischage tray which has been moved to either the left or right. Then, the discharged sheet is slipped downward on the sheet discharge tray due to the sheet own weight so as to be arranged by coming into contact with a sheet end receiving member which is located at a rear end of the sheet discharge tray, thereby enabling of classification and stacking.
In such classifying tray apparatus, a falling distance of the top sheet on the sheet discharge tray is different from that of the bottom sheet to be stacked on the sheet discharge tray after stacking many sheets. The falling distance indicates a distance between the sheet discharging portion and the top sheet stacked on the sheet discharge tray. For example, the first discharged sheet on the sheet discharge tray and the 200th discharged sheet have respective different falling distance with each other.
Thus, the discharged sheet slides on the sheet discharge tray which has the surface inclined upward or slides on the top sheet stacked on the sheet discharge tray, and each rear end of the slid sheets comes into contact with the sheet end receiving member so as to stop moving. During such process, the discharged sheet deviates in a right-to-left direction with respect to the sheet discharge direction. Accordingly, the tendency of the sheets stacked on the sheet discharge tray is such that the upper sheets are in good order while the lower sheets are of unevenness.
There is known an apparatus wherein a vibration proof rubber is fixed to the sheet end receiving member such that the sheet deviation due to the bound after coming into contact with the sheet end receiving member can be avoided. Such apparatus can improve a little in the degree of unevenness. However, it often occurs that the lower sheets on the sheet discharge tray are still uneven.
There is known another apparatus wherein the sheet discharge tray is moved up and down in accordance with the stacked height of sheets so as to make the falling distance even. However, when the stacked height of sheets becomes higher, there occurs resistance between the sheet and the sheet end receiving member during moving of the sheet discharge tray in the right-to-left direction, thereby presenting the problem that the sheets do not follow up the movement of the sheet discharge tray in the right-to-left direction so as to cause the stacked sheets to be uneven in the right-to-left direction.
The unevenness of the stacked sheets has been avoided in the following manner disclosed in the Japanese examined patent publication No. 4-22826 (1992). More specifically, there is provided a sheet end receiving member made of plate (hereinafter referred to as plate sheet end receiving member) which is movable in a right-to-left direction such that a sheet discharge tray moves in the right-to-left direction according to the movement of the plate sheet end receiving member in the right-to-left direction, thereby avoiding the occurrence of resistance between the sheet and the plate sheet end receiving member during moving of the sheet discharge tray in the right-to-left direction.
However, according to the conventional structure, since the sheet discharge tray and the sheet end receiving member integrally move, the total weight of members to move in the right-to-left direction becomes great, thereby requiring a great driving force for moving the members in the right-to-left direction. Further, the conventional structure requires a space inside the main body of the apparatus for moving the sheet end receiving member in the right-to-left direction.